1. Field of the Invention
This invention relates generally to energy transfer devices and methods and, more particularly, to devices and processes for transcutaneous energy transfer (TET) to a secondary coil implanted in a subject.
2. Related Art
Many medical devices are now designed to be implanted in humans or animals, including pacemakers, defibrillators, circulatory assist devices, cardiac replacement devices such as artificial hearts, cochler implants, neuromuscular simulators, biosensors, and the like. Since many of these devices require a source of power, inductively coupled transcutaneous energy transfer (TET) systems are coming into increasing use. A TET system may be employed to supplement, replace, or charge an implanted power source, such as a rechargeable battery. Unlike other types of power transfer systems, TET systems have an advantage of being able to provide power to the implanted electrical and/or mechanical device, or recharge the internal power source, without puncturing the skin. Thus, possibilities of infection are reduced and comfort and convenience are increased.
TET devices include an external primary coil and an implanted secondary coil, separated by intervening layers of tissue. The two coils constitute a transcutaneous transformer. The transformer is designed to induce alternating current in the subcutaneous secondary coil, typically for transformation to direct current to power the implanted device. TET devices therefore also typically include an oscillator and other electrical circuits for periodically providing appropriate alternating current to the primary coil. These circuits, referred to for convenience herein as xe2x80x9cTET primary circuits,xe2x80x9d receive their power from an external power source.
Generally, the non-implanted portions of conventional TET systems are attached externally to the patient, typically by a belt or other fastener or garment, such that the primary coil of the TET is operationally aligned with the implanted secondary coil. The TET primary circuits and external power supply are also generally attached to the patient""s body at or near the site of the attachment of the primary coil. Such a configuration typically is disadvantageous, however, particularly when the patient is sleeping or resting. For example, if a patient is sleeping on a mattress, the patient would likely be uncomfortable, or restricted in movement, if all or some of the TET primary circuits and external power supply were attached to the patient. In addition to discomfort or restriction of movement, additional disadvantages of such body attachments include possibilities of injury to the patient or the devices. Movements of the patient may alter the position of the primary coil so that it is not properly positioned over the implanted secondary coil to achieve a desired or required transfer of power.
To overcome these drawbacks, other conventional approaches require only the primary coil be attached to the patient. Wires connect the primary coil to the TET primary circuits, which, with the power supply, may be located at a distance from the patient outside of the sleeping or resting surface. However, such an alternative configuration also has significant disadvantages. First, the primary coil is still attached to the patient and therefore subject to the above drawbacks may cause discomfort or restriction of movement. Also, as the patient moves, the wires connecting the externally attached primary coil to the TET primary circuits may become tangled or entangled with bedding or the patient. In addition to being uncomfortable, such tangling may result in dislodging the primary coil from its required alignment; it may injure the patient, such as by restricting blood or oxygen supply; or it may interfere with tubes or other devices attached to the patient.
To overcome the above and other drawbacks to conventional systems, the present invention provides an electromagnetic field source (EFS) for providing electromagnetic energy to a secondary coil. In one embodiment, the EFS includes two or more primary coils that each carry a time-varying current to produce an electromagnetic field. The EFS also includes a controller that selectively provides current to one or more of the primary coils based on their position relative to the secondary coil. The controller may be implemented in electrical circuits, software, firmware, or any combination thereof.
In another embodiment, the invention provides a transcutaneous energy transmission (TET) device including a secondary coil implanted in a human being. In this embodiment, the secondary coil is used to provide power for the operation of an implanted medical device, such as an artificial heart or ventricular assist device. In some implementations, the primary coils are housed in furniture, such as a bed mattress. Also, the primary coils may be housed in bed covering, such as a blanket or mattress pad.
In certain embodiments the controller includes a proximity detector that identifies a quantity of primary coils that are closest to the secondary coil, referred herein to as the xe2x80x9cclosestxe2x80x9d primary coils. A current director that is responsive to the proximity detector is also included in the controller. The current director selectively directs time-varying currents through the closest primary coils.
One advantage of a TET in accordance with certain aspects of the present invention is that there are no wires connecting the subject of the implanted device to external components, such as a power supply or other electrical circuits. Rather, a recipient of the implanted device may rest on furniture that houses the primary coils, and those primary coils that are closest to the implanted secondary coil may be energized. Thus, the recipient is uninhibited with respect to movement on or in the furniture, such as a bed, couch, or chair, and is provided with a more comfortable resting environment. Also, serious disadvantages of known systems, such as becoming entangled with a wire, or of dislodging a primary coil, are avoided by the present invention.
Another advantage is the portability of implementations such as those in which the primary coils are housed in a bed covering or a mattress pad. Thus, a recipient may pack such housing, together with the controller and power supply, in suitcases or similar containers for traveling. Similarly, a hospital mattress may readily be converted to include portions of a TET by covering it with a blanket or mattress pad containing primary coils in accordance with embodiments of the present invention.
Advantageously, the primary coils may be disposed over substantially all of the top surface of the mattress, or throughout the bed covering or mattress pad. Thus, in such embodiments, if the recipient shifts position on the mattress, there will be one or more primary coils located close to the implanted secondary coil. In some implementations, the primary coils may be positioned in generally even rows and columns with respect to the top surface of the mattress. In other implementations, they may be positioned generally in hexagonal arrangements. It will be understood to those of ordinary skill that there are many possible configurations that provide primary coils over the entire surface upon which the recipient is resting or reclining.
Also advantageously the controller of the EFS or TET may determine the approximate distance between the primary coils and the secondary coil, and adjust the amount of current to the closest primary coils accordingly. In particular, a proximity detector may be included to determine an approximate distance between one or more of the closest primary coils and the secondary coil. In embodiments that include such a proximity detector, if that distance is greater than a nominal threshold value, current director may increase the currents through selected ones of the closest primary coils. For example, if the recipient is sleeping on a pillow or is otherwise raised above the mattress, the distance from the implanted secondary coil to the primary coils in the mattress may be greater than normal (i.e., greater than when the recipient is sleeping directly on the mattress). By increasing the amount of current directed to the closest primary coils, the electromagnetic fields of the closest primary coils are increased to reach the secondary coil so that it may provide power to the medical device or to an energy storage device. In one embodiment of the EFS or TET, the proximity detector identifies a predetermined number of the closest primary coils. Alternatively, the quantity of closest primary coils may be identified by the proximity detector based on the size of the secondary coil.
The primary coils may be disposed in their housings in accordance with a wide variety of geometric schemes or arrangements. For example, the primary coils may be disposed in a single plane, or in two or more parallel planes. It should be understood that the specification herein of this, and other, geometric arrangements may be approximate. For example, it generally is not required that the primary coils be disposed precisely in a single or parallel planes, in precisely a square pattern, and so on. Rather, they may be approximately so disposed. Similarly, a second-layer primary coil need not be precisely aligned with first-layer primary coils, as described below.
In one embodiment in which a configuration of two parallel planes is used, dead zones of electromagnetic fields generated by one or more primary coils of a first plane are encompassed by electromagnetic fields generated by primary coils in a second plane that is parallel to the first plane. The term xe2x80x9cdead zonexe2x80x9d is used herein to refer to a space in which an electromagnetic field generated by a primary coil is not effective in energizing a secondary coil disposed in that space. This term is further explained, and is illustrated, below. The word xe2x80x9cenergize,xe2x80x9d and its grammatical variants, is used herein to refer to the provision of current to a primary coil so that it produces an electromagnetic field. The word xe2x80x9cencompassedxe2x80x9d is used herein in this context to refer to the covering of the dead zone by the electromagnetic field of a second layer of primary coils, such that the electromagnetic field is effective in energizing the secondary coil disposed in the dead zone of a first layer of primary coils.
In some embodiments having primary coils disposed in two parallel planes, a first plane includes two or more mutually adjacent first-plane primary coils. The term xe2x80x9cmutually adjacentxe2x80x9d means that each of two or more primary coils in a group is adjacent to each of the other primary coils in that group. Examples of such arrangements are the placement of the centers of the primary coils at the comers of a rectangular or triangular shape in the first plane. In such embodiments, a second plane is provided that has at least one second-plane primary coil (not to be confused with a secondary coil). These coils are positioned so that the projection of a magnetic center of the second-plane primary coil on the first plane is approximately equidistant from magnetic centers of each of the two or more mutually adjacent first-plane primary coils. For example, if first-plane square primary coils are positioned so that their comers are adjacent to each other, then a second-plane primary coil is placed in the second plane such that the projection of its magnetic center onto the first plane aligns with the comers of the first-plane square. The term xe2x80x9cmagnetic centerxe2x80x9d of a coil is used herein to mean the geometric center of iso-magnetic contours representing the magnetic field generated by the coil. In a particular implementation of such an arrangement, the first plane has four mutually adjacent primary coils positioned in a roughly square arrangement. The second plane has one primary coil positioned so that the projection of its geometric center on the first plane is approximately centrally located among the four first-plane primary coils.
In some embodiments, the EFS or TET also includes an orientation detector, coupled to the current director, that determines the orientation of the plane of the secondary coil with respect to the planes of the closest primary coils. In some implementations, the orientation detector is electrically coupled to the primary coils and determines the orientation of the plane of the secondary coil utilizing a resonance frequency shift detector. The detector compares shifts in inductance of two or more primary coils due to the proximity of the secondary coil. In other implementations, the orientation detector may determine the plane of the secondary coil utilizing an optical sensor, a mechanical sensor, electromagnetic transmission, or any combination of these or other sensors now or later developed.
In some embodiments, if the orientation detector determines that the secondary coil is disposed in a plane predominantly parallel to the planes of the closest primary coils, the current director directs time-varying currents to flow through the closest primary coils so that each current flows in the same direction. In one implementation of such an embodiment, the quantity of closest primary coils may be simple one coil. In particular, there may be a single closest primary coil if the proximity detector determines that the secondary coil is proximate to an electromagnetic field of the one closest primary coil, not including a dead zone. In another implementation, the quantity of closest primary coils is two or more when all of the primary coils are disposed in the same plane and the proximity detector determines that the secondary coil is proximate to a dead zone of the one closest primary coil.
If the orientation detector determines that the secondary coil is disposed in a plane predominantly perpendicular to the planes of the closest primary coils, the current director directs time-varying currents to flow through the closest primary coils so that a current in each closest primary coil flows in a direction opposite to a direction of a current in an adjacent closest primary coil. In one implementation in which the secondary coil is perpendicularly positioned, the quantity of closest primary coils is two.
The EFS may also include a power supply that is coupled to the controller and that provides current to the primary coils. It should be understood that the power supply may not be directly coupled to the primary coils, but that intermediary components, such as a regulator, may be present. Alternatively, the regulator or other components may be included in the power supply.
In further embodiments, the invention provides a method for providing electromagnetic energy to a secondary coil. The method includes disposing primary coils, each constructed and arranged to carry a time-varying current to produce an electromagnetic field, and selectively providing current to the primary coils based on their position with respect to the secondary coil. In some implementations, such selection includes identifying a quantity of the primary coils that are closest to the secondary coil, and selectively directing time-varying currents through the closest primary coils.
In other embodiments, the invention is a cardiac-assist device including pumping means and a transcutaneous energy transmission (TET) device. The TET includes a secondary coil implanted in a subject, primary coils that carry a time-varying current to produce an electromagnetic field, and a controller that selectively provides current to one or more of the primary coils based on their position with respect to the secondary coil. The pumping means may include a total artificial heart or a ventricular assist device. More generally, the invention provides in some embodiments an organ-assist device including such a TET and an internally implanted organ-assist component.
In yet further embodiments, the invention is an article of furniture having embedded in it two or more primary coils that each carry a time-varying current to produce an electromagnetic field. The furniture also includes a controller that selectively provides current to one or more of the primary coils based on their position with respect to the secondary coil.
Further features and advantages of the present invention as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the drawings, like reference numerals indicate identical or functionally similar elements. Additionally, the left-most one or two digits of a reference numeral identifies the drawing. in which the reference numeral first appears.